This invention relates to charging flowable materials into selected cells of a honeycomb structure and, more particularly, to a method and apparatus for use in selectively sealing cells of a honeycomb structure for the fabrication of filter bodies and other selectively sealed honeycomb structures.
Honeycomb structures having transverse cross-sectional cellular densities ranging from one-tenth to one hundred or more cells per square centimeter, especially when formed from ceramic materials, have several uses, including solid particulate filter bodies and stationary heat exchangers, which require selected cells of the structure to closed by manifolding (i.e. plugging), sealing or other means at one or both of their ends.
It is well known that a solid particulate filter body may be fabricated utilizing a honeycomb structure formed by a matrix of intersecting, thin, porous walls which extend across and between two of its opposing end faces and form a large number of adjoining hollow passages or cells which also extend between and are open at the end faces of the structure. To form a filter, one end of each of the cells is closed, a first subset of cells being closed at one end face and the remaining cells being closed at the remaining opposing end face of the structure. Either of the end faces may be used as the inlet face of the resulting filter. The contaminated fluid is brought under pressure to the inlet face and enters the body via those cells which have an open end at the inlet face. Because these cells are closed at the outlet end face of the body, the contaminated fluid is forced through the thin, porous walls into adjoining cells which are sealed at the inlet face and open at the outlet face of the filter body. The solid particulate contaminant in the fluid which is too large to pass through the porous openings in the walls is left behind and a cleansed fluid exits the filter body through the outlet cells for use.
Rodney Frost and Irwin Lachman describe in a copending application, Ser. No. 165,646, filed July 3, 1980, now abandoned, a most efficient solid particulate filter body formed from a honeycomb structure in which the cells are provided in transverse, cross-sectional densities between approximately one and one hundred cells per square centimeter with transverse, cross-sectional geometries having no internal angles less than thirty degrees, such as squares, rectangles, equilateral and certain other triangles, circles, elipses, etc. The cells are also arranged in mutually parallel rows and/or columns. Alternate cells at one end face are closed in a checkered or checkerboard pattern and the remaining alternate cells are closed at the remaining end face of the structure in a reversed pattern. Thus formed, either end face of the filter body may be used as its inlet or outlet face and each inlet cell (open at inlet face and closed at outlet face) shares common thin porous walls with only adjoining outlet cells, (open at outlet face and closed at inlet face) and vice versa. Other cellular cross-sectional geometries and other patterns of sealed cells may be employed to fabricate effective, although perhaps less efficient filter bodies than those of Frost and Lachman.
For the mass production of such filters, it is highly desirable to be able to seal selected cell ends as rapidly and as inexpensively as possible. Frost and Lachman in the previously referred to application Ser. No. 165,646 describe fabricating filter bodies by manifolding the end of each cell individually with a hand-held, single nozzle, air actuated sealing gun. The manifolding of individual cells by this process is long and tedious and is not suited for the commercial production of such filters and other honeycomb structures which may have thousands of cells to be selectively closed. Frost and Lachman also postulate the use of an array of sealant nozzles so that the sealing mixture may be simultaneously injected into a plurality or all of the alternate cells at each end face of the honeycomb structure. However, a working model of this device is not known to exist for plugging honeycomb structures having these higher cell densities.
In a related area, Noll, et al in U.S. Pat. No. 4,410,591, describe alternate methods of fabricating a multiple flow path body such as a stationary heat exchanger. A honeycomb structure is provided having its cells arranged in columns across its open end faces, an open end face of a honeycomb structure is dipped into a flowable resist material and the resist material removed from selected columns by cutting it away together with the common walls of the adjoining cells in the selected column or, alternatively, the walls between the adjoining cells of the selected columns are cut away at the open end face of the structure before dipping the end face into the flowable resist material and the resist material is blown from the selected columns using compressed air directed down the selected columns where the adjoining cell walls had been removed. The end face was thereafter dipped into a slurry of cement to form a sealed channel across each of the selected columns. The remaining flowable resist material was subsequently removed by heating. As the cross-sectional density of cells in the honeycomb structure is increased, for example to improve the efficiency of a filter body, the tolerances needed for the removal of adjoining cell walls required by the Noll, et al method tighten. The problem is particularly heightened when the manifolded body is fabricated from extruded ceramic or ceramic based honeycomb structures as the present state of the ceramic extrusion art cannot provide perfectly parallel rows and/or columns of cells. Also, the Noll, et al method requires the partial destruction of adjoining cell walls and is entirely unsuited for the fabrication of filter bodies where the cells are sealed in a checkered or other possible alternating cell patterns at the end faces.